There is known a distance measuring device called LIDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging). The distance measuring device irradiates laser light on a measurement target object and converts the intensity of reflected light reflected by the measurement target object into a time-series digital signal on the basis of an output of a sensor. Consequently, the distance to the measurement target object is measured on the basis of a time difference between a point in time of emission of the laser light and a point in time corresponding to a peak of a signal value of the digital signal. Environment light such as sunlight scattered by an object is also made incident on the sensor. The environment light is noise that occurs at random. As processing in the digital signals for reducing such noise that occurs at random, a method of accumulating a plurality of digital signals at random is generally known.
When the distance measuring device is mounted on a mobile body such as a car, the number of times of irradiation of laser light on one measurement point is sometimes limited. In such a case, a plurality of digital signals based on laser lights irradiated in adjacent directions are accumulated and noise reduction processing is performed. However, if a digital signal based on reflected light from an object different from the measurement target object is accumulated, it is likely that an S/N ratio of the accumulated digital signals is reduced and measurement accuracy is deteriorated.